Licensing their engine is just a side business for Epic and I’d bet on average their not getting anything even close to 5% (all their bigger clients should have custom agreements). But that’s fine for them since they’re making loads of money from Fortnite with much less effort (than you would need to make anything similar from just a game engine).

I’m not sure how the overall quality compares, but I’d expect Unity’s users to be way more critical even if it had more bugs just because of all the indie/small developers who’d fall below the 1mil threshold for Unreal but have to pay for Unity.